Stroke is a cardiovascular disease affecting the blood vessels supplying blood to the brain. There are four main types of stroke: two caused by blood clots or other particles, and two by hemorrhage. By far the most common causes for strokes are cerebral thrombosis and cerebral embolism, which are caused by clots or particles that plug an artery. The remaining two are cerebral and subarachnoid hemorrhages caused by ruptured blood vessels.
Stroke is the third leading cause of death in the United States. It kills more than 150,000 people annually and accounts for about one of every 15 U.S. deaths. Stroke is a major source of disability in the developed countries and regions. Typically, ischemic damage, i.e., a lack of oxygen, due to a disruption of the blood supply to a region in the brain is diagnosed as a stroke when accompanied by neurological or other symptoms. In an ischemic stroke, focal ischemia exhibiting a defined region of tissue damage is observed, which is often surrounded by a penumbral region that is susceptible to additional damage over time. When blood supply to the brain is reduced below a critical threshold, a cascade of biochemical events leads to irreversible damage to neurons and brain infarction. Research on treatment and prevention of ischemia is extensive but unfortunately it remains at a basic stage and no adequate therapies are yet in practice.
Stroke is defined as a sudden impairment of body functions caused by a disruption in, e.g., the supply of blood to the brain. For instance, a stroke occurs when a blood vessel bringing oxygen and nutrients to the brain is interrupted by any method including low blood pressure, clogging by atherosclerotic plaque, a blood clot, or some other particle, or when a blood vessel bursts. Because of the blockage or rupture, part of the brain fails to get the blood flow that it requires. Brain tissue that receives an inadequate supply of blood is said to be ischemic. Deprived of oxygen and nutrients, nerve cells and other cell types within the brain begin to fail, creating an infarct (an area of cell death, or necrosis). As nerve cells (neurons) fail and die, the part of the body controlled by those neurons cannot function either. The devastating effects of ischemia are often permanent because brain tissue has very limited repair capabilities and lost neurons are not usually replaced. The blood supply disruption resulting in a stroke may be due to, inter alia, presence of a blood clot, arteriosclerosis, artherosclerotic plaque (or its components), and the like. Thus, treatment for a stroke has to be, preferably, provided rapidly to avoid irreversible damage. The treatment also has to be in agreement with the underlying cause because, for instance, administering agents to inhibit blood coagulation in a stroke due to a hemorrhage risks increasing the damage by promoting hemorrhage. If the stroke is due to the presence or formation of a blood clot, then treatments are directed to dissolve or otherwise reduce the clots.
Cerebral ischemia may be incomplete (blood flow is reduced but not entirely cut off), complete (total loss of tissue perfusion), transient or permanent. If ischemia is incomplete and persists for no more than ten to fifteen minutes, neural death might not occur. More prolonged or complete ischemia results in infarction. Depending on the site and extent of the infarction, mild to severe neurological disability or death will follow. Thus, the chain of causality leading to neurological deficit in stroke has two principal components: loss of blood supply, and cell damage and death.
Thrombosis is the blockage of an artery by a large deposit that usually results from the combination of atherosclerosis and blood clotting. Thrombotic stroke (also called cerebral thrombosis) results when a deposit in a brain or neck artery reaches occlusive proportions. Most strokes are of this type.
Embolism is the blockage of an artery or vein by an embolus. Emboli are often small pieces of blood clot that break off from larger clots. Embolic stroke (also called cerebral embolism) occurs when an embolus is carried in the bloodstream to a brain or neck artery. If the embolus reaches an artery that is too small for it to pass through, it plugs the artery and cuts off the blood supply to downstream tissues. Embolic stroke is the clinical expression of this event.
Once deprived of blood, and, hence oxygen and glucose, brain tissue may undergo ischemic necrosis or infarction. The metabolic events thought to underlie such cell degeneration and death include: energy failure through ATP depletion; cellular acidosis; glutamate release; calcium ion influx; stimulation of membrane phospholipid degradation and subsequent free-fatty-acid accumulation; and free radical generation.
Knowledge of these underlying events has led investigators studying certain types of ischemic injury to utilize agents such as calcium channel blockers, glutamate and glycine antagonists, CDP-amines, free radical scavengers/antioxidants, perfluorocarbons and thrombolytic agents to improve cerebral blood flow and/or neurological outcome, all with mixed results. Certain calcium-channel blockers have been reported to produce inconsistent results and undesirable side effects, such as reduction in pulse or perfusion pressure. See, e.g., Kaste, M. et al. Stroke (1994) 25:1348-1353.
Glutamate antagonists have been observed to reduce infarct size under certain experimental conditions. See, e.g., Olney, J. W. et al. Science (1991) 254:1515-1518. However, most, if not all, of these compounds cause brain vacuolization and most produce phencyclidine-like subjective effects in animals and humans. Ingestion of phencyclidine has been associated with euphoria, anxiety, mood lability and prolonged psychosis.
Although perfluorocarbons have shown some benefit in the outcome from ischemic stroke, these compounds have an extremely long half-life and must be infused into the brain and spinal fluid. In addition, these compounds have been observed to cause gonadal hypertrophy. See, Bell, R. D. et al. Stroke (1991) 22:80-83.
Thrombolytic agents, such as t-PA (tissue plasminogen activator), streptokinase, and urokinase, have shown some promise in the treatment of ischemia. However, these agents have the propensity to increase intracranial bleeding, which, ultimately, can lead to increased mortality. See, e.g., del Zoppo, G. J. et al. Seminars in Neurology (1991) 11(4):368-384; The Ancrod Stroke Study Investigators, Stroke (1994) 25:1755-1759; Hacke, W. et al. Stroke (1995) 26:167. Moreover, the efficacy of these agents may be limited to treatment within the first three hours of stroke.
Free radical scavengers/antioxidants are a heterogenous group of compounds. In general, the effects of these compounds on infarct volume have been inconsistent. For example, superoxide dismutase inhibitors have been found to reduce infarct volume only when injected intracerebroventricularly. See, Kinouchi, H. et al. Proc. Natl. Acad. Sci. USA (1991) 88:11158-11162. Other compounds, such as lubeluzole, have been shown to have clinical benefit but with a very narrow margin of safety. See, Diener, H. C. et al. Stroke (1995) 26:30.
Free radicals, particularly free radicals derived from molecular oxygen, are believed to play a fundamental role in a wide variety of biological phenomena. In fact, it has been suggested that much of what is considered critical illness may involve oxygen radical (“oxyradical”) pathophysiology (Zimmerman, J. J. (1991) Chest 00:1895). Oxyradical injury has been implicated in the pathogenesis of pulmonary oxygen toxicity, adult respiratory distress syndrome (ARDS), bronchopulmonary dysplasia, sepsis syndrome, and a variety of ischemia-reperfusion syndromes, including myocardial infarction, stroke, cardiopulmonary bypass, organ transplantation, necrotizing enterocolitis, acute renal tubular necrosis, and other disease. Oxyradicals can react with proteins, nucleic acids, lipids, and other biological macromolecules producing damage to cells and tissues, particularly in the critically ill patient.
Many free radical reactions are highly damaging to cellular components, i.e., they crosslink proteins, mutagenize DNA, and peroxidize lipids. Once formed, free radicals can interact to produce other free radicals and non-radical oxidants such as singlet oxygen (1O2) and peroxides. Degradation of some of the products of free radical reactions can also generate potentially damaging chemical species. For example, malondialdehyde is a reaction product of peroxidized lipids that reacts with virtually any amine-containing molecule. Oxygen free radicals also cause oxidative modification of proteins (Stadtman, E. R. (1992) Science 257:1220).
In order to prevent the damaging effects of free radicals and free radical-associated diseases, great efforts have been made to develop new antioxidants that are efficient at removing dangerous oxyradicals, particularly superoxide and hydrogen peroxide, and that are inexpensive to manufacture, stable and possess advantageous pharmacokinetic properties, such as the ability to cross the blood-brain barrier and penetrate tissues. Although enhancement of the tolerance of cerebral tissue to ischemia/reperfusion injury has been a goal to complement or replace agents that restore or promote blood flow, clinical trials have so far failed to identify a safe and effective neuroprotectant. Promising neuroprotectant candidates that do not cause unacceptable adverse side effects are almost non-existent. At present, there is no neuroprotectant drug that may be administered by the patient (even with the assistance from relatives) prior to hospital arrival. The reasons include: requirement of intravenous loading dose, adverse effects, narrow therapeutic time window, and potentially serious side effects in patients without stroke or with hemorrhagic stroke. Thus, treating a hemorrhagic stroke with clot fighting agents is likely to seriously exacerbate the damage.
Thus, there is a need for versatile and effective new pharmaceutical compositions comprising antioxidants and free radical scavengers, that limit the extent or otherwise treat nerve cell death (degeneration) such as may occur with ischemic injury.
In addition, while many antioxidant and free radical scavenger compositions are known in the art, a significant limitation of the prior art compositions is their inability to effectively penetrate the blood brain barrier, thus limiting the effectiveness of the prior art compositions in treatment of cerebral ischemic injury.
2,6-diisopropyl phenol (2,6-diisopropylphenol, formula I), is a short-acting hypnotic agent, effective for induction and maintenance of anesthesia (see, e.g., Rees et al., Annu. Rep. Med. Chem., 31, 41-50 (1996), and Trapani et al., Curr. Med. Chem., 7, 249 (2000)). 2,6-diisopropyl phenol also is used for intravenous (IV) sedation by target-controlled infusions (see, e.g., Leitch, Br. Dent. J., 194, 443 (2003)). It is highly lipid-soluble and has a characteristic property that it can readily permeate biomembranes such as blood brain barrier (BBB).

2,6-diisopropyl phenol has been used in the treatment of pathologies relating to the presence of free oxygen radicals (see, e.g., U.S. Pat. Nos. 5,308,874 and 5,461,080). 2,6-diisopropyl phenol has been shown to repair neural damage caused by free oxygen radicals in vitro (see, e.g., Sagara et al., J. Neurochem., 73, 2524 (1999) and Jevtovic-Todorovic et al., Brain Res., 913, 185 (2001)) and has been used in vivo to treat head injury (see, e.g., Kelly et al., J. of Neurosurgery, 90, 1042 (1999)). Furthermore, 2,6-diisopropyl phenol is considered an alternative to barbiturates for the management of refactory status epolepticus (Rossetti, et al., 2004, Epilepsia, 45(7):757-763).
There is evidence suggesting that 2,6-diisopropyl phenol can protect endothelial cells against oxidative stress by inhibiting eNOS transcription and protein expression (see, e.g., Peng et al., Chin. Med. J. (Engl)., 116(5), 731-5 (2003)). Moreover, 2,6-diisopropyl phenol enhances ischemic tolerance of middle-aged hearts, primarily by inhibiting lipid peroxidation (see, e.g., Xia et al., Cardiovasc. Res., 59, 113 (2003)).
It has now been found that 2,6-diisopropyl phenol and its analogs act as antioxidants and free radical scavengers, and can effectively penetrate the blood brain barrier. 2,6-diisopropyl phenol and its analogs are thus useful for the treatment or prevention of cellular damage in various tissues from injuries associated with ischemia, and hence they are useful for the treatment or prevention of injuries of reperfusion in acute cerebral infarction due to abnormal generation of active oxygen species.
The invention provides novel 2,6 diisopropyl phenol compositions and analogs with antioxidant or neuroprotective activity effective for the treatment of ischemic injury. Also provided is a method for timely treatment of a sudden onset of at least one neurological deficit in a subject. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.